Organ rejection is the process whereby a patient's own immune system recognizes the cell surface markers (antigens) within a transplanted organ as foreign (Joosten et al., 2003, Transpl Int, 2003 16, 137-45). Immunologic recognition of foreign cell surface antigens leads to destruction of the foreign tissue: in the case of transplanted organs, the chronic rejection process destroys the functionality of the transplant. Class I or class II “major histocompatibility (MHC)” antigen on the surface of the transplanted organ's cells are processed and presented to the host immune system. Classic initiation of rejection occurs when class II molecules are expressed and activate T-helper (CD4+) lymphocytes. Cytokines thus released by activated CD4+ cells, lead to margination and recognition of foreign class I molecules by cytotoxic T lymphocytes (CD8+, CTL) (Buckley, R. H. J Allergy Clin Immunol, 2003.111, S733-44). This process has been controlled with current pharmacotherapy to the point of reducing acute rejection episodes to around 10% within 1 year after transplantation (Ciancio, G., et al., Transplantation, 2004 77, 244-51). However, most anti-rejection medications are toxic to the patient and given long-term, may induce organ toxicity (Baran, D. A., et al. Am J Cardiovasc Drugs, 2004 4, 21-9) and malignancy (Ganschow, R., et al., J Pediatr Gastroenterol Nutr, 2004 38, 198-203) in some patients. Tolerance in transplantation is the process by which a transplant is performed and maintained without the need for exogenous drugs to prevent rejection.
Infection also presents a significant obstacle to successful transplantation. Despite the use of novel antiviral and antibiotic therapeutics, opportunistic infections continue to add to the morbidity and mortality associated with transplantation. Herpes viruses, as an example, account for serious disease in as many as 50% of transplant recipients (Aiello, F. B., et al., Mod Pathol, 2004.17, 189-96) and this leads to poor outcomes for many of the infected patients. These viruses incorporate their genome into the cells of a transplanted graft and as such, the transplanted organ serves as a reservoir for reactivation and infection in the transplant recipient. Hepatitis C virus leads to cirrhosis and is the most common cause of liver failure amongst patients awaiting liver transplantation. Recurrence of the Hepatitis C in the transplanted liver occurs 100% of the time and leads to graft failure (Neumann, U. P., et al., Transplantation, 2004 77, 226-31) and death in nearly 10% of these patients. CMV and Hepatitis C are just two examples of viruses that cause poor outcomes in transplant patients.
Successful transplantation is also limited by ischemic injury (lack of oxygen) to the transplanted organ as it is removed from a donor. Islet cell transplantation, as an example, is dependant upon high yield of viable islets separated from a cadaver pancreas. Islet viability is diminished as a result of apoptosis (programmed cell death) initiated by insults such as ischemia induced in the organ procurement process. There are current strategies that are being employed in genetically altering islets to prevent such ischemic loss (Fenjves, E. S., et al., Transplantation, 2004 77, 13-8). Islets from Balb/c mice have been transduced with a replication-deficient adenovirus expressing wild-type Survivin (pAd-Survivin; G. P. Basadonna, PhD. Thesis of Charlotte Ariyan, MD. Yale Univ. 2003). Survivin, first described in some human cancers, is a gene related to bcl-2 or the baculovirus IAP (inhibitor of apoptosis) gene (Ambrosini, G., C., et al. Nat Med, 1997.3, 917-21), but functions independently (Adida, C, et al., Lancet, 1998 351, 882-3). Recombinant expression of Survivin counteracts apoptosis in B lymphocyte precursors (Ambrosini, G., C., et al. Nat Med, 1997 3, 917-21). While not normally expressed in adult cells, Survivin expression can and does occur. Enhanced expression of Survivin has been consistently associated with inhibition of apoptosis, in vitro (Kobayashi, K., et al., Proc Natl Acad Sci USA, 1999 96, 1457-62; Tamm, L, et al., Cancer Res, 1998 58, 5315-20; Mahotka, C, et al. Cancer Res, 1999 59, 6097-102; Suzuki, A., et al., Oncogene, 2000 19, 1346-53; Islam, A., et al., Med Pediatr Oncol, 2000 35, 550-3) and in vivo (Grossman, D., et al., J Clin Invest, 2001 108, 991-9).
In spite of continuing advances in transplantation technology, serious morbidity and mortality are still associated with transplantation. Genetic alteration in many ways can be harnessed to improve transplantation outcomes; however, genetic alteration of tissue has thus far been most effectively performed through use of viral intermediaries (such as adenoviral transfection). Such use of viral vectors continues to present a serious danger to transplant patients; and a safer, efficacious method of preventing rejection of transplanted tissues is highly desirable.